A circuit is composed of individual devices, such as resistors, transistors, capacitors, diodes, etc., interconnected by metal conductors (e.g., wiring) through which electric current can flow. The combination of devices and wiring allows various simple and complex operations to be performed: voltages can be converted, signals can be amplified, computations can be performed, data can be moved from one place to another, etc. Integrated circuits are circuits that are fabricated on a wafer made of a semiconducting material. Silicon is the typical semiconducting material used in wafers. Once fabrication is complete, the wafer is cut into many pieces (i.e., dies), with each die containing a copy of the integrated circuit.
Integrated circuit (IC) fabrication includes two process portions: a front-end-of-line (FEOL) portion followed by back-end-of-line (BEOL) portion. Individual devices (e.g., transistors, capacitors, diodes, etc.) are formed in the semiconductor wafer during FEOL. FEOL involves several sequential steps including masking, etching, doping, etc., and others well known in the art. FEOL generally covers everything up to (but not including) the creation of metal interconnect layers.
BEOL is the second portion of IC fabrication where devices formed during FEOL are interconnected with metal wiring to create a circuit. BEOL generally begins when the first layer of metal is deposited on the wafer. BEOL includes the formation of contacts or vias, insulating layers (e.g., dielectrics), metal wiring, and bonding sites. Ten or more metal interconnect layers, each having vias, insulating layers, metal wiring, etc., can be added during BEOL. The top-most metal interconnect layers usually have the thickest, widest and most widely-separated metal wiring, which make them very well suited for power or ground distribution since they have the least resistance.